Heterotopic ossification (HO) is a complication occurring after THA which can lead to postoperative pain and reduced function. Non-selective NSAIDs are commonly used in the prophylaxis of heterotopic ossifications after THA. The exact mechanism of prevention of bone formation is unclear. Some results indicate that the development of HO follows a Cox-2 pathway. A further aim of this clinical trial is to investigate the efficacy of Etoricoxib in the prevention of heterotropic ossification.